(1) Field of the Invention
The present invention is directed to the field of cylinder locks and particularly to side bar type locks Specifically, the present invention relates to reducing the size and manufacturing cost of cylinder locks without sacrificing the security provided thereby. Accordingly, the general objects of the present invention are to provide novel and improved devices and methods of such character.
(2) Description of the Prior Art
Various types of cylinder locks are known in the prior art. Cylinder locks are comprised of a key plug rotatably mounted within a cylinder. Normally the locking mechanism prevents rotation of the key plug. The locking mechanisms of prior cylinder locks may be generally characterized as having either tumblers or side bars. These types of locking mechanisms function along similar principles.
Tumbler type locking mechanisms are comprised of a plurality of tumblers reciprocally mounted within the key plug. The tumblers, which may be in the form of pins, are typically spring biased across the shear line between the key plug and the cylinder so as to normally engage the cylinder. This prevents the key plug from rotating within the cylinder. However, one type of prior art tumbler locking mechanism incorporates pin type tumblers associated with cylinder mounted drivers which are biased against the tumblers. These drivers are of cylindrical shape as are the pin tumblers. The drivers, not the tumblers, are normally biased across the shear line. The drivers and tumblers may be separated across the shear line by a properly fitted key; the key conventionally having a plurality of cuts at different levels. These cuts urge the tumblers against the drivers causing the two to be separated across the shear line thereby allowing the key plug to be rotated.
Another tumbler type locking mechanism incorporates flat slidable tumblers which are biased cross the shear line. These flat tumblers are provided with posts at varying positions along their length which, when contacted by properly formed key cuts, urge the tumbler across the shear line so that the key plug may be rotated.
Side bar type locking mechanisms incorporate a slidable fence which is positioned within a lateral slot of the key plug and is normally biased into engagement with the cylinder to prevent the key plug from rotating. The individual tumblers, which are reciprocally mounted within the key plug and also engage the cylinder, are provided with grooves or true gates at different locations. These true gates are capable of receiving the fence when in alignment therewith. When all the tumblers are properly positioned by the keys, and thus retracted from engagement with the cylinder, the fence is in alignment with all the true gates. Rotation of the key plug forces the fence to engage the true gates and thus release the lock. The proper positioning of each tumbler is produced by a key which has properly fitted key cuts at the required levels.
One specific class of prior art cylinder lock which utilizes drivers and pin tumblers is generally referred to as the KABA lock. In KABA type locks the key is provided with detents instead of key cuts. These detents are depressions within the opposed side surfaces of the key that have a proper depth to correctly position the tumblers. The use of KABA type locks is attractive because the key has detents instead of cuts which eliminates the sharp cutting edges.
It has also been proposed to fabricate cylinder locks which employ both pin-type tumblers and side bars; the two locking mechanisms being separately activated by a complex key having key cuts with angled surfaces. These locks are, however, quite complex and thus relatively expensive.
The above-discussed prior art cylinder locks have had one or more disadvantages. For example, locking mechanisms which incorporate drivers and pin tumblers are susceptible to tampering. The susceptibility to being defeated results from the fact that manufacturing tolerances result in the key plug being rotatable a limited distance within the cylinder. This creates a shoulder at the shear line. When the drivers are moved past the shear line they are caught by this shoulder. By minutely rotating the plug and pushing the drivers outward from the keyway all the drivers may be caught and the plug fully rotated to open the lock.
A major disadvantage with cylinder locks incorporating either tumbler or side bar locking mechanisms resides in the comparatively high manufacturing cost. In order to provide numerous key changes in locks employing tumbler type locking mechanisms numerous sizes of pin tumblers and drivers must be manufactured or numerous flat tumblers having posts positioned at different positions along their lengths must be provided. Similiarly, to provide for key changes in the case of side bar locking mechanisms numerous tumblers having true gates positioned at differing locations must be manufactured. The requirement of manufacturing and stocking many different tumblers greatly increases the cost of each individual lock.
The prior art KABA locks only incorporate locking mechanisms which use driver and pin tumbler arrangements. As stated above locks which incorporate drivers and pin tumblers are subject to tampering and have disadvantageous manufacturing costs. Further, these prior art KABA locks are relatively large in size since bores must be provided within the lock cylinder in order to accomodate the drivers and springs. Thus the usefulness of prior art KABA locks is limited by the driver and pin tumbler locking mechanism.
An additional disadvantage shared by prior side-bar type locks and locks of the KABA type resides in the inability to remove the key at any rotational position of the key plug. The ability to remove the key at various positions is necessary for most switch type lock applications.